Safety device for stamping machines



April 29, 1969 H sc ET AL I 3,440,909

SAFETY DEVICE FOR STAMPING MACHINES Filed April 13, 1967 v INVENTOR3 H. clvm A. E F77cfz Adm W 7f%; (ML-4;)

United States Patent U.S. Cl. 83-61 7 Claims ABSTRACT OF THE DISCLOSURE A safety device for a stamping machine having elements to stop the machine when a stamped waste piece is not correctly ejected and is left behind in a corresponding opening in a main punch. This takes place as to the stopping of the machine when a member should fail to take up its predetermined position of rest upon the completion of a working cycle of the machine.

This invention relates to a safety device, for a stamping machine comprising: a main punch and the corresponding die for stamping workpieces from a piece of material; at least two hole punches within the die for punching holes directly through the workpieces with the punches passing through into openings in the main punch; ejector pins which can move lengthwise through the openings in the main punch for ejecting the punched-out waste pieces from the corresponding openings in the main punch; an ejector piston operated by fluid under pressure for operating the ejector pins; and a stop for limiting the travel of the ejector piston.

Stamping machines of this type operate very well so long as the punched-out waste pieces are correctly ejected by the ejector pins from the openings in the main punch after every cycle of operation. However, if only one such waste piece remains lodged in the corresponding opening in the main punch, what normally happens is that the ejector pin concerned undergoes deformation and is damaged, so that it jams in the opening in the main punch. Then, during the next cycle of operation, another waste piece is forced into the opening and may result in the main punch being so damaged that it can no longer be used.

There is therefore a need for a safety device to prevent damage such as described and which automatically stops the stamping machine if any one of the punched-out waste pieces should 'be left behind in the corresponding opening in the main punch. This raises many considerable technical problems where there are two or more hole punches within the die of the stamping machine. In such cases, each hole punch has hitherto required a safety device of its own, which has made the construction expensive and resulted in comparatively high fault liability.

The object of the present invention is to overcome this difiiculty by providing a simple but reliable safety device of the kind just described.

The safety device according to the invention, for a stamping machine of the type referred to in the preamble, is mainly characterised by the provision of an intermediate member interposed between the ejector piston and the ejector pins, to all of which latter it is common and which, in relation to the ejector piston, when this is at the limit of its travel, can be moved along the ejector pins by gravity or by at least one spring to a predetermined position of rest, so long as no punched-out waste piece is lodged in any opening in the main punch. A further object of the invention resides in a means of exploring the intermediate member and determining Patented Apr. 29, 1969 whether it is or is not in its pre-determined position of rest. Another object of the invention resides in a control swltch operated by the exploring means whereby the stamping machine is stopped if the intermediate member should fail to take up its pre-determined position of rest upon the completion of each working cycle of the mac ine.

Further features and details of the invention will become apparent from the following description of one example of a machine embodying the inventive principle when considered in connection with the accompanying drawing, which shows, by way of example only, a diagrammatic vertical section of a stamping machine equipped with a safety device in accordance with the invention.

The stamping machine as shown on the drawing has a stationary machine table 10, below which the main punch 11 is provided. This punch is rigidly housed in a top force block 12 and is surrounded by a pressure plate 13, in the form of a frame or ring on which a V-sectioned rim 14 (also known as a catch ring )is formed. The pressure plate 13 is secured to the bottom ends of guiding end fixing rods 15, the other ends of which are attached to a disc-shaped thrust member 16 housed above the force block 12 within a recess 17 in the machine table 10. The rods 15 form a sliding fit in corresponding holes in the force block 12 and in part of the punch 11. The thrust member 16 is surrounded by a thrust ring 18 which is housed within the recess 17 in the machine table 10 and held in place by the force block 12.

Below the machine table 10 and the punch 11, a working ram 21 has motion imparted to it hydraulically, by means not shown in the drawing, so that it moves upwards and downwards, guided by a vertical column 20. The top end of the ram 21 carries the bottom force block 22, into which is recessed a die 23, acting in conjunction with the punch 11. The die 23 is ring-shaped, so that the punch 11, which fits it, can pass into it when the ram 21 moves upwards. The punch 11 and the die 23 serve to stamp out a workpiece S from a flat piece of material M. Within the die 23 is a counter-member 24, which is secured by guiding and fixing rods 25, so as to follow the motion of a counter-ram 26. This ram 26 fits coaxially within a longitudinal cavity in the working ram 21, in relation to which it can be moved hydraulically to eject the workpiece S from the die 23. A thrust ring 27 which surrounds the counter-ram 26, is housed in a corresponding recess in the working ram 21 and held in place by the force block 22.

Between the thrust ring 27 and the die 23 there is a recess in the force block 22, housing a backing block 28, and a plate 29 through both of which pass the guiding and fixing rods 25. The free length of the rods 25 is greater than the combined vertical depth of the backing block 28 and the plate 29, so that a certain amount of up-and-down movement of the counter-ram 26, the rods 25 and the counter-member 24 is possible. The plate 29 serves to secure two or more hole punches 30, positioned within the die 23 so as to slide lengthwise through the counter-member 24. The hole punches 30 serve to punch holes L, of the desired shape and size, in the desired positions in the workpiece S, these punches entering the corresponding openings 31 in the main punch 11 during the stamping method.

For ejecting the waste pieces B, produced by the hole punches, from the openings 31 in the main punch 11, each of these openings 31 contains an ejector pin 32, which has longitudinal motion and also passes through the force block 12. The top ends of all the ejector pins 32 bear against the thrust member 16. To prevent the ejector pins 32 from dropping out of the openings 31, each ejector pin has a projecting shoulder 33, seating against the upper side of the main punch 11.

On the upper side of the machine table is fixed a hollow cylinder or cowling 35 in which an ejector piston 36 can slide up and down. Between the piston 36 and the thrust member 16, a substantially cylindrical intermediate member 37 is interposed, which fits into and has vertical motion within an opening in the machine table 10. The diameter of the intermediate member 37 and this guide opening in the table 10 is smaller than the diameter of the ejector piston 36, so that this, as it moves downwards encounters a stop 38 on the machine table 10, which prevents any further downward movement. The thrust member 16 and the intermediate member 37 are common to all the ejector pins 32 and transmit the downward motion of the ejector piston 36 to all the ejector pins 32.

The combined vertical depth of the thrust member 16 and the intermediate member 37 is smaller by a short distance K than the distance between the stop 38 and the upper face of the force block 12. In principle, therefore, the intermediate member 37 can continue to move downwards, to the extent of the distance K, when the ejector piston 36 is up against the stop 38, the member 37 thus taking up a pre-determined position of rest, as shown in the left-hand half of the drawing. In the example shown, this takes place partly by gravity and partly by the action of compression springs 39 accommodated in recesses between the piston 36 and the intermediate member 37. According to circumstances, however, the springs 39 could be dispensed with, the force of gravity alone being relied on. The intermediate member 37 is connected to the ejector piston 36 by a central pin 40, which is fixed to the piston 36 by a screw 41. The pin 40 has a retaining shoulder 42 thereon, which engages below the opposing shoulder 43 on the intermediate mem ber 37, so as to prevent the latter from dropping out when the force block 12 and the thrust member 16 are removed from the stamping machine. The two shoulders 42 and 43 working together, however, are so placed that limited relative movement, to the extent of the distance K, is possible between the intermediate member 37 and the ejector piston 36.

The cylindrical peripheral face of the intermediate member 37 contains a peripheral groove 44, of trapezoidal cross-section. The lower face 45 of the groove 44 offers a sloping control surface for operating a senser pin 46, which is free to slide longitudinally in a passage 47 in the machine table 10, at right angles to the axis of the cylindrical intermediate member 37. In this passage 47 there is also provided a compression spring 48, which holds the senser pin 46 constantly pressed against the intermediate member 37. The groove face 45 and the senser pin 46 are so placed in relation to each other that the latter is moved longitudinally by a distance equal to the depth of the groove 44 when the intermediate member is moved upwards through the distance K from its pre-determined position of rest (left, in the drawing). The senser pin 46 and the spring 48 serve to determine whether the intermediate member 37 is or is not in its pre-determined position of rest. The senser pin has a conical face 49 worked transversely thereon, which acts as a control surface and operates a pressure pin 51, fitted with a roller 50. This pin operates an electrical control switch 52 of any known design, which is secured to the machine table 10 with the aid of an angle bracket 53.

The control switch 52 is incorporated in an electrical circuit (not shown) in such a way that it brings the stamping machine automatically to a halt if, on completion of any cycle of operation, the intermediate member 37 fails to return to its pre-determined position of rest, shown in the left-hand half of the drawing.

The intermediate member 37, senser pin 46, spring 48, pressure pin 51 and control switch 52 together form a safety device for protecting the stamping machine ag inst da g s o d a punch-out waste piece B become 4 lodged in the corresponding opening 31 in the main punch 11.

The mode of operation of the stamping machine described and of the safety device first described is as follows:

At the start of every cycle of operation of the machine, the various parts of the latter are in the positions shown in the left-hand half of the drawing. A strip of material M, strip sheet metal for example, is placed between the main punch 11 and the die 23. The working ram 21 then rises, whereupon the counter-member 24 first moves towards the strip of material M from underneath and forces it against the face of the punch 11. As the working ram continues to move upwards, the counter-member 24 and the parts 25 and 26 connected to it, remain stationary. The die 23 presses the strip of material M against the pressure plate 13, so that the rim 14 bites into the material M, to prevent it from moving sideways. By means of the die 23, the pressure plate 13 is then moved slightly upwards, thus causing the thrust member 16, by the guiding and fixing rods 15, also to be raised similarly within the opening 17 in the machine table 10. Thus, by the combined action of the die 23 and the main punch 11, the workpiece 8 is cut out of the strip of material M. At the same time, the hole punches 30 strike through the workpiece S and the corresponding waste pieces B are forced into the openings 31 in the main punch 11. As this takes place and is completed, the ejector pins 32 are able to withdraw upwards, because, as stated, the thrust member 16 is raised by the pressure plate 13 and the rods 15. As the thrust member 16 rises, the intermediate member 37 and the ejector piston 36 are also moved upwards. The oblique face 45 in the groove in the intermediate member 37 moves the senser pin 46 in opposition to the action of the spring 48. The resulting operation of the control switch 52 of this moment, however, has no effect on the running of the stamping machine.

The working ram 21 subsequently moves down into the position illustrated, following which the counter-ram 26 moves upwards in relation to the working ram 21, thus causing the workpiece S to be ejected from the die 23 by means of the rods 25 and the counter-member 24. A fluid under pressure is admitted to the hollow cylinder 35, above the ejector piston 36, which it drives downwards as far as the stop 38. The ejector piston 36 also drives the intermediate member 37 and the thrust member 16 downwards. The result of this is, first, that the strip of material M is stripped from the main punch 11 by the rods 15 and the pressure plate 13 and, second, that the waste pieces B are ejected by the ejector pins 32 from the corresponding openings 31 in the main punch 11.

So long as the waste pieces B are correctly ejected, the intermediate member 37 will be moved by the force of gravity and by the springs 39 a further distance K d0wnwards when the ejector piston 36 is up against the stop 38, since the ejector pins 32 are not opposed by any considerable resistance such as to prevent this further movement. When the thrust member 16 rests on the force block 12, the intermediate member 37 has reached its predetermined position of rest, shown in the left-hand half of the drawing. Immediately before this, the oblique face 45 of the groove in the intermediate member 37 will have moved past the senser pin 46, allowing it to be thrust by the spring 48 into the peripheral groove 44 in the intermediate member 37. The control switch 52 will thereupon have returned to its initial position, a control signal thus being given to enable the stamping machine to continue running for a further cycle.

However, should any waste piece B become lodged in the corresponding opening 31 in the main punch 11, because, for instance, the ejector pin 32 concerned has been distorted, as shown in the right-hand half of the drawing, the action of gravity and of the spring 39 will n0 longer sufiice to move the intermediate member 37 to its predetermined position of rest, away from the ejector piston 36. The oblique face 45 of the groove cannot then reach the senser pin 46, which is therefore unable to drop into the groove 44, so that the control switch 52 cannot return to its original position. Hence, the signal already mentioned, which would allow the stamping machine to continue running, is not given, so that the machine is automatically stopped before the start of a fresh cycle. In conjunction with this, it is of advantage for a visual or audible signal to be given, to tell the supervising staff that the stoppage of the machine has been brought about by the control switch 52 and that the ejector pins 32 and the openings 31 in the main punch 11 need examination.

The main advantages of the safety device on a stamping machine, as illustrated and described, are that the device is of simple design and not very expensive, is independent of the number of ejector pins 32 to be watched over, need not be removed or altered when the stamping tools are changed, and is highly reliable in operation. A further advantage is that the safety device will also stop the stamping machine automatically if, for any reason, the pressure plate 13 is prevented from moving down to its starting position and the strip of material M is not correctly stripped from the main punch 11.

The safety device here described can naturally also be used on stamping machines other than the one illustrated, for example, on a machine in which the die is stationary and the main punch moves or in which the die is overhead and the main punch is below.

Instead of the mechanical means 46 and 48 shown, other means such as, for example, photo-electric devices (a light-sensitive cell or the like), may be provided for exploring the intermediate member 37 and determining whether it is or is not in its pre-determined position of rest.

We claim:

1. A stamping machine comprising: a main punch having openings and the corresponding die for stamping workpieces from a piece of material; at least two hole punches within the die for punching holes right through the workpieces, said punches passing through into the openings in the main punch; ejector pins capable of moving length- Wise through the openings in the main punch, for ejecting punched-out waste pieces, from the corresponding openings in the main punch; an ejector piston for operating the ejector pins; a stop for limiting the travel of the ejector piston; and a safety device comprising an intermediate member interposed between the ejector piston and the ejector pins, to all of which latter it is common, and which in relation to the ejector piston, when this is up against the stop, can be moved along the ejector pins by a force to a pre-determined position of rest, so long as no punched-out waste piece is lodged in any opening in the main punch; means for exploring the intermediate member and determing whether it is or is not in its pre-determined position of rest; and a control switch operated by the said means whereby the stamping machine is stopped if the intermediate member should fail to take up its pre-determined position of rest upon the completion of each working cycle of the machine.

2. A stamping machine according to claim 1, in which the said means comprises a senser pin with transverse motion, which is thrust sideways by a Spring against the intermediate member and can be moved by an oblique control surface on the intermediate member immediately before the intermediate members takes up its pre-determined position of rest, and in which the senser pin is arranged to operate the control switch.

3. A stamping machine according to claim 1, in which the said means comprises a senser pin with transverse mo tion, which is thrust sideways by a spring against the intermediate member and can be moved by an oblique control surface on the intermediate member immediately before the intermediate member takes up its pre-determined position of rest, and in which the senser pin is arranged to operate the control switch, and the control surface of the intermediate member forms one side of an inner peripheral groove in the intermediate member.

4. A stamping machine according to claim 1, in which the said means comprises a senser pin with transverse motion, which is thrust sideways by a spring against the intermediate member and can be moved by an oblique control surface on the intermediate member immediately before the intermediate member takes up its pre-determined position of rest, and in which the senser pin is arranged to operate the control switch, and the control switch having an operating member acted on by an oblique control surface on the senser pin.

5. A stamping machine according to claim 1, in which the intermediate member is connected to the ejector piston by at least one pin which permits a limited movement of the intermediate member between the ejector piston and a retaining shoulder on said pin, longitudinally in relation to the ejector pins.

6. A stamping machine according to claim 1, in which the force is one created by gravity.

7. A stamping machine according to claim 1, in which the force is one created by at least by one spring.

References Cited UNITED STATES PATENTS 2,589,849 3/1952 Oetiker 83-61 2,970,503 2/ 196 1 Chevallier 83-61 FOREIGN PATENTS 1,005,517 9/ 1965 Great Britain.

WILLIAM S. LAWSON, Primary Examiner.

US. Cl. X.R. 83123, 128, 620 

